1. Field of Invention
The present invention relates to a pharmaceutical composition for the treatment and prevention of liver fibrosis and cirrhosis. Specifically, the present invention relates to a pharmaceutical composition for the treatment and prevention of liver fibrosis and cirrhosis, comprising 5-(2-pyrazinyl)-4-methyl-1,2-dithiol-3-thione (oltipraz) and dimethyl-4,4′-dimethoxy-5,6,5′,6′-dimethylene dioxybiphenyl-2,2′-dicarboxylate (DDB) as major active ingredients.
2. Description of Related Art
Liver plays a key role in the metabolism of xenobiotics and metabolism of endogenous substances and is an important organ with consistent enzymatic reactions and energy metabolism. Among many chronic diseases in Korea, hepatitis, cirrhosis, and liver cancer are the most widespread and life threatening diseases next to cardiovascular diseases. As Korea has a relatively large population of drinkers when compared to developed countries, and as the liver injuries resulting from binge drinking are fairly high, a lot of attention has been paid to treat liver diseases. Often chronic liver damage resulting from viral infection or alcohol drinking causes cirrhosis or liver cancer. In consideration of the physiological characteristics and significance of liver tissues, and in light of the importance of treating and preventing liver diseases, demand is high for the ultimate development of therapeutic and preventive drugs against liver damage.
Various substances, including several synthetic compounds and galenical preparations, show hepatoprotective functions both in vitro and in vivo. Although it has been known that silymarin or betaine have liver protective effects with the action mechanism of cytokine inhibition and increase in the level of glutathione, a curative effect would be hard to expect because of its low effectiveness. As no appropriate curative agents against liver diseases are currently available, the said agents are frequently used for clinical trials. Malotilate and its derivatives, the indication of which is the treatment of liver fibrosis, protect the liver from toxic chemicals and the possible mechanism of action include the induction of phase II conjugating enzymes and the inhibition of cytochrome P450s. However, the compounds non-selectively inhibit several cytochrome P450s and show only preventive effect.
It is known that several substituents of sulfur containing dithiolthione which naturally occurs in cruciferous vegetables, have liver protecting effects. Among them, oltipraz was used as a curative agent against schistosomiasis with the following formula.

Oltipraz increases cellular thiol content and induces the expression of enzymes responsible for maintaining the glutathione (GSH) pool and detoxifying the tissue from electrophilic molecules. The activities of the following enzymes are increased by oltipraz: NAD(P)H quinone reductase, microsomal epoxide hydrolase, glutathione S-transferase (GST) and UDP-GT. In particular, GST protects the liver from some toxic chemicals such as carbon tetrachloride or acetaminophen (Ansher S S, Dolan P, and Bueding E. Chemoprotective effects of two dithiolthiones and of butylhydroxyanisole against carbon tetrachloride and acetaminophen toxicity. 1983 Hepatology 3,932–935).
Furthermore, oltipraz inhibits chemical carcinogenesis caused by benzo[a]pyrene, NDEA, and uracil mustard as well as aflatoxin B1-induced hepatic tumorigenesis and azoxymethane-induced colon carcinogenesis (Bolton M G, Munoz A, Jacobson L P, Groopman J D, Maxuitenko Y Y, Roebuck B D, and Kensler T W. Transient intervention with oltipraz protects against aflatoxin-induced hepatic tumorigenesis. 1993, Cancer Res. 53, 3499–3504).
The known inhibitory mechanisms of carcinogenesis by oltipraz are the followings. First, oltipraz increases the level of an antioxidant, reduced GSH, in tissues. Second, it inhibits bioactivation of carcinogens by inhibiting phase I enzymes such as cytochrome P450. Third, it promotes detoxification of carcinogens by inducing phase II detoxifying enzymes including GST and UDP-GT. Fourth, oltipraz inhibits replication of the human immunodeficiency virus (HIV) type I in vitro. Fifth, it removes reactive intermediates in cells by increasing thiol levels and promotes DNA repair. It has been reported that oltipraz increases GSH levels in most tissues and removes free radicals generated by radiation or xenobiotics. It also has been known that oltipraz functions as a protective agent against radiation by helping to maintain cellular homeostasis.
In regards to the above description, more detailed information will be set out below. Cancer is uncontrolled cell growth and differentiation presumably caused by DNA damages in somatic cells (Cancer Biology, 3rd ed. Raymond W. Ruddon, pp. 61–95, 497–507, Oxford Press). Anticancer effects of chemical agents primarily rely on their anti-mutagenesis effects or their activity in suppressing transformation into cancer cell or proliferation of cancer cells. Oltipraz has been studied as a cancer chemopreventive agent (Ansher et al., 1983; Bolton et al., 1993). Cancer chemopreventive effects of oltipraz is associated not only with inhibition of cytochrome P450 3A, but also with induction of phase II detoxifying enzymes. Expression of glutathione S-transferase (GST) is increased by oltipraz in cells and animals (Clapper et al., 1994; Davidson et al., 1990), which is associated with suppression in toxicant-induced tissue injuries and carcinogenesis (Kensler et al., 1987; Maxuitenko et al., 1998). Oltipraz protects the liver against tissue damage caused by radiation (Kim et al., 1997), and GST induction known from the prior study means cellular adaptive response. Oltipraz also protects the liver against toxicants (Ansher et al., 1983). Inhibition of aflatoxin B1-induced carcinogenesis by oltipraz is mediated through the intervention of cytochrome P450 3A-catalyzed metabolic activation of carcinogen. According to recent clinical trials, oltipraz was effective in lowering plasma aflatoxin B1 levels of people at high risk of liver cancer. Aflatoxin B1-induced carcinogenesis in animals was also reduced by the application of oltipraz.
It has been reported that oltipraz inhibits hepatitis B virus (HBV) replication in 2.2.15 cells, which were infected with HBV DNA-containing plasmid. Therefore, oltipraz inhibits transcription of hepatitis B virus gene, elevates p53 protein expression (Chi et al., 1998), and inhibits human immunodeficiency virus (HIV) replication (Prochaska et al., 1995).
Cinical trials in regard to the chemopreventive effect of oltipraz against liver carcinogenesis has been conducted in China. The results showed that oltipraz had weak protective effects against liver carcinogenesis. It is also known that oltipraz protects the liver against toxicant-induced hepatotoxicity, at least moderately. In addition, the safety of oltipraz has been proven in toxicity studies performed in rats and dogs (Fund. Appl. Toxicol. 1997 January; 35(1):9–21).
DDB (dimethyl-4,4′-dimethoxy-5,6,5′,6′-dimethylene dioxybiphenyl-2,2′-dicarboxylate), a component derived from Shizandrae, is a curative agent for the treatment of hepatitis clinically used in East Asia, including Korea. DDB protects the liver tissue against carbon tetrachloride-, galactosamine-, thioacetamide- or prednisolone-induced injuries and enhances antibody production. Having been known to be effective in clinical trial for the patients with hepatitis, DDB is used widely in the clinical setting. The present inventors reported that DDB's pharmacological effect was associated with the inhibition of NF-κB activation and TNF-β production. Further, it was found that DDB did not affect the expression of drug metabolizing enzymes. Since NF-κB is known as a transcription factor mediating the inflammatory response, an inhibitor of NF-κB would be capable of inhibiting systemic inflammatory response.
Liver fibrosis means a prepathological state wherein damaged liver tissues in chronic liver diseases such as hepatitis are not repaired into normal tissues, but are converted to fibrous tissues such as collagen as part of an in vivo adaptive response.
Although liver fibrosis is outcome of an in vivo repair process in response to tissue damage, damaged liver tissues are replaced by fibrous tissues, which can no longer function normally (e.g. in vivo metabolism or bile juice production). As continuous and recurring liver fibrogenesis leads to cirrhosis and eventually causes death, it is crucial to develop new drugs to treat liver fibrosis. However, as the precise mechanism of liver fibrogenesis is not known, appropriate curative drugs have not yet been developed.
Recent studies revealed that transforming growth factor-beta (TGF-β), a cytokine secreted from Kupffer and Ito cells in the liver, was an important mediator in liver fibrosis. In addition, it was reported that blocking TGF-β activity by employing TGF-β antibodies, antisense RNA, and modifications to TGF-β receptors significantly decreases liver fibrosis. However, the effects of said research have only been confirmed at the experimental level. Clinical viable drugs for liver fibrosis and cirrhosis have not been reported.